Role of ERK1/2 in fsh-induced PCNA expression and steroidogenesis in granulosa cells

Follicular development is characterized by both proliferation and differentiation of granulosa cells (GCs) under the control of FSH. However, the cellular mechanism by FSH is not known. Using cultured GCs, we examined whether FSH-activated ERK1/2 was involved in the regulation of the proliferation- related gene proliferating cell nuclear antigen ( PCNA) and steroidogenesis. GCs were obtained from the ovaries of DES-treated immature rats and cultured in serum-free medium. The results showed that FSH activated ERK1/2 in a time-dependent manner, with a peak at 20 min. Such activation was PKA-dependent as was inhibited by specific inhibitors. FSH induced PCNA expression in a time-dependent manner, with a maximum stimulation at 2 h. Similarly, StAR and steroid levels increased as FSH treatment time extended, with a maximum progesterone and StAR production at 48 h. ERK1/2 inactivation by UO126 inhibited the stimulatory effects of FSH on both PCNA and StAR expression and steroid synthesis in the GCs ( p less than 0.01). Immunocytochemical studies further revealed that ERK1/2 inhibition led to a reduction of mitochondrial StAR in the GCs by FSH. These observations suggested that the stimulation of FSH on PCNA expression and steroidogenesis in GCs was mediated at least partially by ERK1/2.